Books: As man carves out more and more space for himself and his pursuits, the species we share the world with are getting squeezed out, says author David Quammen.

David Quammen likes to write about "small, peculiar facts connected to large ideas."

That's what he did in the science column he wrote for 15 years in Outside magazine. And that's what he's done in his new book, "The Song of the Dodo" (Scribner).

This time, Quammen got the small, peculiar fact for it before he got the large idea. "About 10 years ago I read a newspaper story . . . about the extinction of native birds on the island of Guam," he said.

They were disappearing, starting in the south of the island and moving north until a number of native species found nowhere else were all gone. Why was a puzzle.

At the same time, power outages were occurring with increasing frequency. Another mystery--or was it a clue?

In both cases, the culprits turned out to be snakes.

This is probably what happened: During World War II, American forces sweeping through the Pacific inadvertently brought from New Guinea and other islands the brown tree snake. It climbs trees and moves through the tropical forest from branch to branch, eating unsuspecting birds as it goes.

There had been only one tree-climbing snake on Guam before, and the birds had evolved to cope with it. On the brown tree snake's native grounds, a number of competitors kept it under control.

But on Guam the snake had no serious competitors and no predators, so it multiplied rapidly and gobbled up the birds that had evolved without defenses against it. The birds, like the dodo, were "ecologically naive."

The power outages were the consequence of the snakes treating power lines as if they were tree branches.

Quammen, 48, a former Yale man and Rhodes scholar with a short, neat ponytail and an Oxford doctorate on William Faulkner, now had his "small, peculiar fact." Were there large ideas to be connected to it?

"As I started looking for a broader scientific context," he said, "working in libraries, doing background reading, I found a huge body of information on what is called island biogeography: the science of what lives where.

"Island biogeography is the study of islands or any other isolated patch of landscape--for example, a forest surrounded by fields. This might sound obvious, but it's an important biological insight."

The fathers of island biogeography were Charles Darwin and Alfred Russel Wallace. Both working in the 19th century from their experience with life on islands, they separately developed the theory of evolution by natural selection.

In its modern manifestation the fast-growing field can be traced to a "dense little volume" titled "The Theory of Island Biogeography," published in 1967 by the late Robert MacArthur of Princeton and Edward O. Wilson, now of Harvard.

"It was a daring, fruitful and provocative attempt by two young men to merge biogeography with ecology and transform them into a mathematical science," Quammen writes.

That is the subject of Quammen's book. He spares the reader most of the mathematics, but merely points out that it leads to such concepts as the larger the island, the more species it will have; the smaller, the fewer.

And once the definition of "island" is expanded to include patches of wilderness surrounded by freeways or wetlands hemmed in by townhouse developments, the connection between humans' progress and other species' extinction becomes clear.

The great point is that man is chopping up the planet's ecosystems into smaller and smaller pieces--like the Amazon rain forest or the grizzly bear habitat of the American West. As he chops, the number of species drops.

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Quammen describes the main point of island biogeography:

"Islands are especially conducive to evolution," he said, citing bizarre forms of life like the Galapagos Islands' unique swimming iguana.

Likewise, "Islands are especially conducive to extinction," because they tend to be relatively small and isolated.

Therefore, ominously: "Islands are diagnostic, because the world is being chopped into islands."

But when Quammen came upon MacArthur and Wilson's "dense little volume" he hadn't yet decided to do the book.

"I wasn't sure I had enough human dimension and adventure to make it a good read," he says.

Then he read more about Wallace, the English naturalist and island explorer, and his relationship with the better-known Darwin.

Wallace developed his theory of evolution by natural selection while he was exploring the natural world of the Malay Archipelago, now Indonesia. He sent a paper on his discovery to Darwin, on the other side of the world in England.

Darwin, who had conceived of natural selection while brooding at home on the strange creatures he had seen on another group of islands, the Galapagos, had been working for 20 years on a book about his theory. On receiving Wallace's paper, honor would have dictated that Darwin see to its publication immediately. Darwin held it back for a month while, Quammen said, he "cobbled together" a paper of his own and with the help of a friend had the two papers published jointly.